The optical response of the lowest-energy isomers of the B20 family is calculated using time-dependent density-functional theory within a real-space, real-time scheme. Significant differences are found among the absorption spectra of the clusters studied. We show that these differences can be easily related to changes in the overall geometry. Optical spectroscopy is thus an efficient tool to ch...

The process of reversible coloration changes induced at least in one-direction by photoirradiation is referred to as photochromism.1) The two isomers of photochromic compounds differ in their geometrical and electrical structures. These geometrical and electrical differences lead to changes in the physical properties of the molecules, such as their absorption and fluorescence spectra, refractiv...

Stereoisomerism describes those compounds which have the same molecular formula and chemical structure, but the atoms are orientated in a different direction. There are two isomers, each a mirror image of the other, called enantiomers. They are also called optical isomers because they rotate the plane of polarised light either to the right referred to as +, dextro, d or D isomer, or to the left...

IN T RODUC T ION Synthesis and characterization of cyclometalated iridium (III) complexes in organic light emitting display (OLED) applications is of great interest, as these complexes display high emission quantum yields and can be readily colortuned through systematic modification of the ligands using facile syntheses. Depending on the types of ligands surrounding the central iridium atom, th...

In chemistry and physics symmetry principles are all important, for example, leading to the selection rules governing optical transitions. We have investigated the influence of the molecular symmetry on the surface potential landscape of molecules in the limit of weak molecule-substrate binding. For this purpose, the induced lateral motion of Cu(II)-tetraazaphthalocyanine molecules, for which f...

The susceptibility of a wide variety of a-amino acids to the action of Land of n-amino acid oxidases from different biological sources has been studied by a number of investigators (l-7). These studies have in general revealed the considerable differences in the rates of oxidation by these enzymes of amino acids of different chemical structure. It would perhaps be superfluous to undertake even ...

The (R)- and (S)-optical isomers of 9 epoxides, benzyloxymethyloxirane, epichlorohydrin, glycidol, glycidyl 3-nitrobenzenesulfonate, glycidyl 4-nitrobenzoate, glycidyl tosylate, styrene oxide, glycidyl 1-naphthyl ether and glycidyl 4-nitrophenyl ether, have been compared for their in vivo and in vitro genotoxicity. The in vitro short-term test employed was the Ames mutagenicity assay with Salmo...

The effects of optical isomers of ephedrine (EPH) and methylephedrine (MEP) on the twitch response to electrical stimulation (1 msec, 1 Hz) in the isolated rat vas deferens were investigated to clarify the action on alpha 2-adrenoceptors. l-EPH (10(-7) 3 x 10(-5) M) and d-EPH (10(-6)-10(-4) M) markedly inhibited the twitch response in the presence of prazosin (10(-6) M). l-MEP also inhibited th...